Method and system for operating a multi-user multiple-input multiple output (MU-MIMO) wireless communications system

ABSTRACT

A technique for operating a wireless communications system that supports multi-user multiple-input multiple-output (MU-MIMO) communications between a base station and multiple mobile stations involves generating inter-cell interference information at the mobile stations and providing the inter-cell interference information to the base station. The base station uses the inter-cell interference information to calculate channel quality indicators (CQIs) and then makes scheduling decisions in response to the CQIs. Data is transmitted from the base station to the mobile stations according to the scheduling decisions.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.12/452,067, filed Apr. 19, 2010, now U.S. Pat. No. 7,944,906 entitled“METHOD AND SYSTEM FOR OPERATING A MULTI-USER MULTIPLE-INPUT MULTIPLEOUTPUT (MU-MIMO) WIRELESS COMMUNICATIONS SYSTEM.” U.S. patentapplication Ser. No. 12/452 067 is assigned to the assigned of thepresent application and is incorporated by reference into thisdisclosure as if fully set forth herein. This disclosure hereby claimspriority under 35 U.S.C. §120 to U.S. patent application Ser. No.12/452,067.

FIELD OF THE INVENTION

The invention relates generally to wireless communications systems, andmore particularly, to managing channel quality indicators in amulti-user multiple-input multiple-output wireless communicationsnetwork.

BACKGROUND OF THE INVENTION

The 3rd Generation Partnership Project (3GPP) was established to produceglobally applicable technical specifications and technical reports for a3rd generation mobile system based on evolved Global System for Mobilecommunications (GSM) core networks and the radio access technologiesthat they support (i.e., Universal Terrestrial Radio Access (UTRA) inboth Frequency Division Duplex (FDD) and Time Division Duplex (TDD)modes). The scope was subsequently amended to include the maintenanceand development of the GSM technical specifications and technicalreports including evolved radio access technologies (e.g., GeneralPacket Radio Service (GPRS) and Enhanced Data rates for GSM Evolution(EDGE)).

In the 3GPP Long Term Evolution (LTE) specification, when operating inmulti-user multiple-input multiple-output (MU-MIMO) mode, the schedulerof an evolved Node B (eNB) needs channel quality indicators (CQIs) fromthe multiple different user equipments (UEs) to make schedulingdecisions. Conventionally, CQIs are generated at the UEs and transmittedto the eNB. When a wireless system is operated in single-usermultiple-input multiple-output (SU-MIMO) mode, the CQIs can beaccurately calculated by the UEs because the UEs have all of theinformation necessary to calculate the CQIs, which includes theequivalent channel matrix, the usage scheme of each spatial sub-channel,and the inter-cell interference plus additive noise. However, whenoperating in MU-MIMO mode, the UEs do not necessarily know the usagescheme (pre-coding) that will be used in the next transmission timeinterval (TTI) for each spatial sub-channel. In MU-MIMO mode, differentspatial sub-channel usage schemes will result in different intra-cellinterference and consequently different CQIs. In order to account forthe different spatial sub-channel usage schemes that could be used andto take full advantage of multi-user scheduling, the UE would need tocalculate different CQIs for each different spatial sub-channel usagescheme and then provide the different CQIs to the eNB through uplinksignaling. A drawback to calculating multiple different CQIs at each UEand transmitting the multiple different CQIs to the eNB is that theseoperations consume valuable UE processing and uplink signalingresources.

SUMMARY OF THE INVENTION

A technique for operating a wireless communications system that supportsMU-MIMO communications between a base station and multiple mobilestations involves generating inter-cell interference information at themobile stations and providing the inter-cell interference information tothe base station. The base station uses the inter-cell interferenceinformation to calculate CQIs and then makes scheduling decisions inresponse to the CQIs. Data is transmitted from the base station to themobile stations according to the scheduling decisions.

In an embodiment in accordance with the invention, instead ofcalculating a variety of CQIs at each UE, inter-cell interferenceinformation is generated at the UEs and transmitted to the eNB. At theeNB, CQIs are calculated for the UEs using the eNB's knowledge of theequivalent channel matrix and the usage scheme of each spatialsub-channel along with the inter-cell interference information that istransmitted from the UEs. Because the eNB has the inter-cellinterference information from the UEs along with the equivalent channelmatrix and the usage scheme of each spatial sub-channel, the calculatedCQIs accurately reflect the conditions at the UEs. The calculated CQIsare then used to make scheduling decisions at the eNB and data istransmitted between the eNB and the UEs according to the schedulingdecisions. Calculating the CQIs at the eNB instead of at the UEs avoidsthe need to have the UE calculate multiple different CQIs and avoids theneed to burden the uplink channels with carrying those CQIs to the eNB.

Other aspects and advantages of the present invention will becomeapparent from the following detailed description, taken in conjunctionwith the accompanying drawings, illustrating by way of example theprinciples of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts a wireless communications system that supports MU-MIMOcommunications between a base station and multiple mobile stations.

FIG. 2 illustrates a signaling timeline between a base station and amobile station in a wireless communications system in which CQIs arecalculated at the base station instead of at the mobile stations.

FIG. 3 illustrates a signaling timeline between an eNB and a UE in awireless communications system in which CQIs are calculated at the eNBusing inter-cell interference information from the UE, where theinter-cell interference information is provided to the eNB as meanvalues, standard deviations, and an index.

FIG. 4 depicts an eNB and a UE that are configured to operate asdescribed above with reference to FIGS. 2 and 3.

FIG. 5 is a process flow diagram of a method for operating a wirelesscommunications system that supports MU-MIMO communications between abase station and multiple mobile stations.

FIG. 6 is a graph of the number of index bits relative to signal tonoise error.

Throughout the description, similar reference numbers may be used toidentify similar elements.

DETAILED DESCRIPTION

Multi-user multiple-input multiple-output (MU-MIMO) is an advancedspatial multiplexing technique for downlink transmission. FIG. 1 depictsa wireless communications system 100 that includes a base station 102(referred to herein as an evolved Node B (eNB)) and multiple mobilestations 104 (referred to herein as user equipments (UEs)). The wirelesscommunications system is operated in MU-MIMO mode using time divisionduplexing (TDD). In the embodiment of FIG. 1, the eNB is a wirelesscommunications base station that supports MU-MIMO operation as specifiedin the 3GPP Long Term Evolution (LTE) specification. The eNB includesfour antennas 106 although the eNB can include more than four antennas.In the embodiment of FIG. 1, the UEs are wireless communications mobilestations that support MU-MIMO operation as specified in the 3GPP LTEspecification. Each of the UEs has two antennas 108, although the UEsare not limited to two antennas (e.g., the UEs can include only oneantenna or more than two antennas).

In a MU-MIMO wireless communications system that includes Mindependently encoded data streams to be transmitted from an eNB to atmost M UEs, the data symbols to be transmitted at arbitrary time epochcan be expressed as x=[x₁ x₂ . . . x_(M)]^(T), where □^(T) is the vectortranspose. A channel that exists between a transmit antenna and areceive antenna is denoted by an M_(r)×M_(t) complex matrix H, where,M_(t) is the transmit antenna number and M_(r) is the receive antennanumber. The M_(r) receive antennas are distributed among M UEs and eachUE can be equipped with a single antenna or multiple antennas. Eachentity of H denoted by h_(ij) represents the channel gain betweenreceive antenna i and transmit antenna j. In a wireless communicationssystem, such as the wireless communications system 100, which operatesin MU-MIMO mode, the transmitter multiplies the data symbol vector xaccording to a pre-coding matrix E, which is an M_(t)×M matrix. Thegeneral mathematical representation of a wireless communications systemoperating in MU-MIMO mode can be expressed as:y=HEx+z  (1)

Where, y=[y₁ y₂ . . . y_(M) _(r) ] is the signal vector at the receivingantennas of the UEs and z is the inter-cell interference plus additivenoise, where the inter-cell interference plus additive noise is referredto herein simply as inter-cell interference. In addition, the pre-codingmatrix is usually expressed in column format as E=[e₁ e₂ . . . e_(k) . .. e_(M)], where e_(k)(k)=1, 2, . . . M) is an M_(t)×1 column vector andeach column in E is referred to as a “codeword.” Further, HE can beexpressed as H′=[h′₁ h′₂ h′₃ . . . ] and is referred to as theequivalent channel matrix. The columns of H′ are referred to as spatialsub-channels since they are the actual vector channels that carry theuser data.

When wireless communications systems use channel-dependent scheduling toexploit multi-user diversity, a scheduler at the eNB needs to know thechannel quality indicator (CQI) of each UE in advance. In the 3GPPspecifications, the CQI is expressed as an integer index. In oneembodiment, the CQI is expressed as one of thirty-two CQI indexes witheach CQI index having a corresponding signal-to-noise ratio (SINR)threshold. In an embodiment, a CQI is calculated by calculating the SINRof a channel and then selecting the CQI index that has the highest SINRthreshold that is less than the to calculated SINR. In order toaccurately calculate the CQI of each UE, the eNB needs three pieces ofinformation: 1) the equivalent channel matrix; 2) the usage scheme ofeach spatial sub-channel (e.g., the size or number of columns, andtherefore the specific selection of the preceding matrix, E, from apre-defined set of candidate pre-coding matrices); and 3) the inter-cellinterference plus additive noise at the UE.

In an embodiment, Minimum Mean Square Error (MMSE) is used by the UEs asthe baseline receiver detection method. A calculation of the detectedsignal at a UE is described below for a wireless communications systemoperating in MU-MIMO mode in which the eNB has four transmit antennas,there are four single-antenna UEs, and all four of the spatialsub-channels are in use. The detected signal can be expressed for a UE,e.g., UE #1, as:y′=h′ ₁ x ₁ +h′ ₂ x ₂ +h′ ₃ x ₃ +h′ ₄ x ₄ +z  (2)

The CQI of the UE can be calculated as:e=Ph′ ₁ ^(H) K _(I) ⁻¹ h′ ₁  (3)where, K _(I)=(Ph′ ₂ h′ ₂ ^(H) +Ph′ ₃ h′ ₃ ^(H) +ph′ ₄ h′ ₄ ^(H) +zz^(H))  (4)

In equation (3), e is the calculated SINR of the received signal whichcan be used to select a CQI index. In equation (4), K_(I) is a temporarymatrix used to calculate the CQI, which is derived from the detectionalgorithm of the MMSE receiver and P is the transmit power on spatialsub-channel h′₁. From equation (4) it can be seen that the calculationof the SINR for a received signal requires knowledge of the equivalentchannel matrix, the usage scheme of each spatial sub-channel, and theinter-cell interference plus additive noise. If any one of theseparameters is not available, the CQI calculation will not be complete.

In conventional MIMO systems, CQIs are calculated at the UEs and fedback to the eNB. When in SU-MIMO mode, the UEs have access to theequivalent channel matrix, the usage scheme, and the inter-cellinterference and therefore the desired CQIs can be calculated at the UEsand fed back to the eNB. However, when in MU-MIMO mode, the usage schemeis known only at the eNB and not provided to the UEs. Therefore, the UEsdo not have all of the information necessary to calculate the CQIs.Specifically, since the usage scheme has a significant impact on theinter-cell interference when a wireless communications system isoperating in MU-MIMO mode, the calculated CQIs will vary significantlydepending on the assumptions that are made with respect to usage schemesfor each spatial sub-channel. To better exploit the multi-userdiversity, each UE would have to calculate multiple CQIs based onvarious different usage assumptions and provide those CQIs to the eNBthrough an uplink channel. The calculation and transmission of multipleCQIs at each UE would significantly impact UE processing and uplinksignaling utilization.

In an embodiment in accordance with the invention, instead ofcalculating a variety of CQIs at each UE, inter-cell interferenceinformation is generated at the UEs and transmitted to the eNB. At theeNB, CQIs are calculated for the UEs using the eNB's knowledge of theequivalent channel matrix and the usage scheme of each spatialsub-channel along with the inter-cell interference information that istransmitted from the UEs. Because the eNB has the inter-cellinterference information from the UEs along with the equivalent channelmatrix and the usage scheme of each spatial sub-channel, the calculatedCQIs accurately reflect the conditions at the UEs. The calculated CQIsare used to make scheduling decisions at the eNB and data is transmittedbetween the eNB and the UEs according to the scheduling decisions.Calculating the CQIs at the eNB instead of at the UEs avoids the need tohave the UE calculate multiple different CQIs and avoids the need toburden the uplink channels with carrying those CQIs to the eNB.

FIG. 2 illustrates a signaling timeline between a base station (e.g.,eNB 102) and a mobile station (e.g., UEs 104) in a wirelesscommunications system 100 (FIG. 1) in which CQIs are calculated at thebase station instead of at the mobile stations. Referring to FIG. 2,inter-cell interference information 110 is generated at a mobile stationand then transmitted from the mobile station to the base station. In anembodiment, the inter-cell interference information includes informationabout the signals that were received at the UE. The base station usesthe inter-cell interference information to calculate a CQI and uses theCQI to make a scheduling decision. In an embodiment, a schedulingdecision may involve both scheduling and resource allocation parametersincluding, for example, the selection of transmission frequencies andspatial sub-channels to use for each UE. Data 112 is then transmittedfrom the base station to the mobile station according to the schedulingdecision.

In an embodiment in accordance with the invention, the inter-cellinterference information is provided to the eNB as mean values, standarddeviations, and an index. In the case in which a UE has two receiveantennas, the inter-cell interference, z, is a 2×1 complex vector thatcan be expressed as: [(a+bi)(c+di)]^(T). The expression includes fourentries a, b, c, and d, which represent the real and imaginary parts ofZ and it can be assumed that both a and b follow Gaussian distributionwith a corresponding mean value (μ₁) and a corresponding standarddeviation (σ₁ 2) and that both c and d follow a Gaussian distributionwith a corresponding mean value (μ₂) and a corresponding standarddeviation (σ₂ 2). In an embodiment, one out of a group of predefinedvectors N={N₀, N₁, . . . N₂ _(K) ⁻¹} (referred to herein as a“codebook”) is used to represent the inter-cell interference, z, whereeach vector is a sample of a Gaussian distribution with zero mean andstandard deviation equal to one. Table 1 is an example of a codebook fora, b, c, and d in which sixteen different codebook entries are uniquelyidentified using a 4-bit index.

TABLE 1 codebook design example of z Index a_(i) b_(i) c_(i) d_(i) 0−0.5 −0.5 −0.5 −0.5 1 −0.5 −0.5 −0.5 +0.5 2 −0.5 −0.5 +0.5 −0.5 3 −0.5−0.5 +0.5 +0.5 4 −0.5 +0.5 −0.5 −0.5 5 −0.5 +0.5 −0.5 +0.5 6 −0.5 +0.5+0.5 −0.5 7 −0.5 +0.5 +0.5 +0.5 8 +0.5 −0.5 −0.5 −0.5 9 +0.5 −0.5 −0.5+0.5 10 +0.5 −0.5 +0.5 −0.5 11 +0.5 −0.5 +0.5 +0.5 12 +0.5 +0.5 −0.5−0.5 13 +0.5 +0.5 −0.5 +0.5 14 +0.5 +0.5 +0.5 −0.5 15 +0.5 +0.5 +0.5+0.5

Referring to Table 1, a 4-bit index of “7” corresponds to the values of:a=−0.5, b=+0.5, c=+0.5, and d=+0.5. The specificity of the codebook is afunction of the number of codebook entries. A codebook with more entriesand thus finer granularity requires an index with more bits to uniquelyidentify each entry and a codebook with fewer entries can be representedwith an index having fewer bits. The size of the codebook isimplementation specific.

In an exemplary operation, each UE calculates the mean value andstandard deviation of both of the signals received at its two antennas.In an embodiment, the mean value and standard deviation for eachreceived signal, μ₁,σ₁ ² and μ₂,σ₂ ², are calculated based on all of theinter-cell interference information measured in a long period (e.g. 1radio frame). In an embodiment, the mean and standard deviation are bothquantized as m×10^(−n), where m is represented by three bits and n isrepresented by three bits. Once calculated, the mean values and standarddeviations are transmitted to the eNB for use in calculating CQIs.

In an embodiment, selecting an index from the codebook involvesnormalizing the inter-cell interference at a particular instant:z=[(a+bi)(c+di)]^(T), toz′=[(a′+b′i)(c′+d′i)]^(T),which follows a standard Gaussian distribution (0,1):

$\left\{ \begin{matrix}{a^{\prime} = \frac{a - \mu_{1}}{\sigma_{1}}} & {b^{\prime} = \frac{b - \mu_{1}}{\sigma_{1}}} \\{c^{\prime} = \frac{c - \mu_{2}}{\sigma_{2}}} & {d^{\prime} = \frac{d - \mu_{2}}{\sigma_{2}}}\end{matrix} \right.$

The normalized inter-cell interference, z′, is then mapped to a nearestvector N_(i) in the codebook as follows:

$i^{*} = {\arg\;{\min\limits_{i = 0}^{2^{K} - 1}{{z^{\prime} - N_{i}}}}}$

Once the index is selected from the codebook, it is transmitted to theeNB. In an embodiment, the index is transmitted to the eNB separatelyfrom the mean values and standard deviations.

Once the eNB receives the mean values, standard deviations, and theindex from a UE as described above, the inter-cell interference, z, canbe regenerated at the eNB. In an embodiment, the inter-cell interferenceis regenerated at the eNB as follows:

$\left\{ {{\begin{matrix}{a^{''} = {{a_{i^{*}} \times \sigma_{1}} + \mu_{1}}} & {b^{''} = {{b_{i^{*}} \times \sigma_{1}} + \mu_{1}}} \\{c^{''} = {{c_{i^{*}} \times \sigma_{2}} + \mu_{2}}} & {d^{''} = {{d_{i^{*}} \times \sigma_{2}} + \mu_{2}}}\end{matrix}z^{''}} = \begin{bmatrix}{a^{''} + {b^{''}i}} & {c^{''} + {d^{''}i}}\end{bmatrix}^{T}} \right.$

For example, assuming that index “7” is fed back to the eNB, theinter-cell interference is regenerated according to the followingexpression:z″=[(μ₁−0.5×σ₁)+(μ₁+0.5×σ₁)i(μ₂+0.5×σ₂)+(μ₂+0.5×σ₂)i] ^(T)

The eNB then uses the regenerated inter-cell interference, z″, tocalculate at least one CQI for the corresponding UE. The eNB then usesthe calculated CQI(s) to make a scheduling decision. Data is transmittedfrom the eNB to the UE according to the scheduling decision.

Since the mean values and standard deviations will change at arelatively low frequency, in an embodiment, the mean values and standarddeviations for the received signals are provided to the eNB on arelatively long interval, e.g. every 10 radio frames, while the index isprovided to the eNB at a relatively short interval, e.g., every TTIwhich is approximately 10 ms in the LTE TDD Type 1 frame structure.

FIG. 3 illustrates a signaling timeline between an eNB and a UE in awireless communications system in which CQIs are calculated at the eNBusing inter-cell interference information from the UE, where theinter-cell interference information is provided to the eNB as meanvalues, standard deviations, and an index. First, the eNB provides theUE with a codebook 120 for use in selecting an index. The codebook couldbe static or semi-static depending on the application. In an embodiment,the codebook is provided to multiple UEs via a broadcast or commoncontrol channel. Next, the UE receives signals from the eNB, measures acharacteristic of the received signals (e.g., signal power), andcalculates the mean value and standard deviation of each receivedsignal. Additionally, the UE selects an index that represents themeasured characteristics of the received signals. The mean values,standard deviations, and index are all transmitted to the eNB. In anembodiment, the mean values and standard deviations 122 are transmittedtogether at a relatively long period (e.g., one data set every 10 radioframes) and the index, i, 124 is transmitted separately at a relativelyshort period (e.g., one index every TTI, e.g., 10 ms in the LTE TDD Type1 frame structure).

The eNB uses the inter-cell interference information, which was providedas mean values, standard deviations, and an index, to calculate a CQI ormultiple CQIs under various usage schemes (e.g., h′₁ h′₂ h′₃ . . . ).The eNB then uses the CQIs to make a scheduling decision or multiplescheduling decisions and user data 126 is transmitted to the UEaccording to the scheduling decision(s). In addition to user data, theeNB may also transmit scheduling and control information 128, which isrelated to the scheduling decision, to the UE.

FIG. 4 depicts functional block diagrams of an eNB 102 and a UE 104,which are configured to implement the above-described technique in aMU-MIMO environment. The eNB includes a codebook module 140, a CQIcalculator 142, a scheduler 144, and a MU-MIMO transmitter 146. Thecodebook module is the source of the codebook that is distributed fromthe eNB to the UE. The CQI calculator calculates CQIs in response to theinter-cell interference information that is received from the UE. Thescheduler makes scheduling decisions using the CQIs that are generatedby the CQI calculator. The MU-MIMO transmitter transmits information,including the codebook, user data, and scheduling and controlinformation to the UE. The UE includes an interference calculator 150, acodebook module 152, an index selector 154, a signal receive andmeasurement module 156, and a transmitter 158. The signal receive andmeasurement module receives and measures signals that are received onthe UE's antennas. The interference calculator calculates the mean andstandard deviation for the received signals in response to measurementinformation generated by the signal receive and measurement module. Thecodebook module stores the codebook and the index selector selects anindex from the codebook in response to the received signals. Thetransmitter transmits the mean values, the standard deviations, and theindex to the base station for use in calculating CQIs. Although only oneUE is shown for description purposes, more than one UE can be supportedby and interact with the eNB. Additionally, although certain functionalelements are shown in FIG. 4, the functions associated with thefunctional elements may be distributed throughout the eNB or the UE.Further, the functional elements may be embodied as hardware, software,firmware, or any combination thereof.

FIG. 5 is a process flow diagram of a method for operating a wirelesscommunications system that supports MU-MIMO communications between abase station and multiple mobile stations. At block 502, inter-cellinterference information is generated at a mobile station. At block 504,the inter-cell interference information is transmitted from the mobilestation to the base station. At block 506, a CQI is calculated at thebase station for the mobile station using the inter-cell interferenceinformation transmitted from the mobile station. At block 508, ascheduling decision is made at the base station in response to the CQI.At block 510, data is transmitted from the base station to the mobilestation according to the scheduling decision.

The above-described technique can be implemented in a manner thatreduces the amount of uplink signaling that is required to operate awireless communications system in MU-MIMO mode relative to conventionaltechniques in which the CQIs are generated at the UEs. For example, in a4×4 MU-MIMO transmission scheme, the eNB has four transmit antennas anda UE has two receive antennas, resulting in four spatial channels. Usinga technique in which the CQIs are generated at the UEs, the resultingfeedback signaling overhead can be calculated as indicated in Table 2.

TABLE 2 Conventional CQI feedback overhead channel channel Preferrednumber number Un-used spatial sub- MCS bits of CQI used for used forchannel channel each feedback UE#1 other UEs number selection bitscombination overhead 1 1 2 2 5 7 1 2 1 2 5 7 2 1 1 2 * 2 5 9 2 2 0 2 * 25 9 Total CQI 7 + 7 + 9 + 9 = 32 bits feedback overhead

As indicated in Table 2, the UE uses two bits to indicate a preferredspatial sub-channel since there are a total of four sub-channelsavailable and if two spatial sub-channels are selected, thecorresponding overhead will be 2*2=4 bits. Additionally, five bits areused to indicate the modulation and coding scheme (MCS) selection. Thus,from Table 2 it can be seen that the total CQI feedback overhead is 32bits in an allocation period, e.g. 10 ms.

Using the technique described above with reference to FIGS. 1-4 toprovide inter-cell interference information to the eNB and assuming themean values and standard deviations are fed back over every 10 radioframes, the overhead related to the mean values and standard deviationsis calculated as 2*2*6=24 bits per 100 ms. Furthermore, assuming acodebook that utilizes a 16-bit index that is fed back in every radioframe (10 ms), the average uplink feedback overhead is calculated as:24/(100/10)+16=18.4 bits per 10 ms. The overhead of 18.4 bits per 10 msrepresents over a 42% reduction in overhead as compared to theconventional technique as described with reference to Table 2.

The CQI calculation error for the technique described with reference toFIGS. 1-4 is compared to an ideal CQI calculation in the graph of FIG.6, which plots the number of index bits on the x-axis against the SINRerror on the y-axis. In the graph of FIG. 6, the codebook ranges in sizefrom four bits to sixteen bits and the relative linear absolute errorbetween the estimated SINR (in linear units) and the accurate SINR isused as the performance metric. As shown in the graph of FIG. 6, theSINR error 160 is very small when the index is more than about twelvebits. The small error reflected in FIG. 6 will tend to improve theaccuracy of MCS selection, and the Block Error Rate (BLER) performancewill likely be close to the ideal scheme.

The above-described technique takes advantage of channel reciprocitybetween the eNB and UEs in the TDD wireless communications system,wherein channel reciprocity involves essentially equivalent channelresponses in the uplink and downlink directions.

Although specific embodiments of the invention have been described andillustrated, the invention is not to be limited to the specific forms orarrangements of parts as described and illustrated herein. The inventionis limited only by the claims.

The current claims follow. For claims not marked as amended in thisresponse, any difference in the claims below and the previous state ofthe claims is unintentional and in the nature of a typographical error.

The invention claimed is:
 1. A method performed by a mobile stationoperative in a wireless communication system, the method comprising:generating inter-cell interference information, wherein generating theinter-cell interference information comprises calculating a mean valueand a standard deviation for multiple signals that are received at themobile station, making signal measurements at the mobile station, andselecting an index from a codebook in response to the signalmeasurements, wherein the index is representative of the measuredsignals, and transmitting the inter-cell interference information to abase station for the calculation, at the base station, of a channelquality indicator (CQI) based on the inter-cell interferenceinformation, wherein the inter-cell interference information provides tothe base station includes the mean value, standard deviation, and theselected index.
 2. The method of claim 1 further comprising receivingthe codebook from the base station, wherein the codebook definesmultiple indexes.
 3. The method of claim 1 wherein generating theinter-cell interference information comprises making signal measurementsat the mobile station, calculating mean values in response to the signalmeasurements, calculating standard deviations in response to the signalmeasurements, and selecting an index from a codebook in response to thesignal measurements.
 4. The method of claim 3 further comprisingproviding the mean values and the standard deviations to the basestation at an interval that is longer than an interval at which theindex is provided to the base station.
 5. A method performed by a basestation usable in a wireless communications system, comprising:receiving inter-cell interference information from at least one mobilestation; calculating a channel quality indicator (CQI) for a mobilestation using the inter-cell interference information received from themobile station, wherein the CQI is calculated at the base station usingequivalent channel matrix information and usage scheme information forspatial sub-channels in addition to the inter-cell interferenceinformation that is received from the at least one mobile station;making a scheduling decision in response to the CQI; and transmittingdata to the mobile station according to the scheduling decision.
 6. Themethod of claim 5 further comprising, at the base station, receivingmean values and standard deviations from the mobile station at aninterval that is longer than an interval at which an index is providedto the base station.
 7. The method of claim 5 further comprising, at thebase station, calculating a CQI related to the mobile station forvarious usage schemes and making a scheduling decision in response tothe calculated CQIs.
 8. A method performed by a mobile station usable ina wireless communications system, the method comprising: receiving andmeasuring multiple incoming signals; generating inter-cell interferenceinformation, wherein generating inter-cell interference informationcomprises calculating a mean value and a standard deviation for thereceived signals, selecting an index from a codebook in response to thereceived signals; and transmitting the inter-cell interferenceinformation to the base station for use in calculating a channel qualityindicator (CQI) at the base station, wherein the mean value and thestandard deviation are transmitted to the base station at an intervalthat is longer than an interval at which the index is transmitted to thebase station.
 9. The method of claim 8 further comprising storing acodebook.